The present invention relates to the electric coupling of an electrode connection to a current output terminal, and in particular a terminal of the “glass-metal bushing” type usually used in small-format electrochemical generators. The invention relates in particular to electrochemical generators intended for portable equipment, the capacity of which is generally less than 20Ah, particularly but not exclusively for sealed lithium generators. The invention moreover extends to the method for producing this coupling.
An electrochemical generator comprises an electrochemical bundle comprising an alternating sequence of positive and negative electrodes framing a separator impregnated with electrolyte. Each electrode most often comprises a metal current collector supporting on at least one of its surfaces the electrochemically active material. The electrode is connected electrically to a current output which ensures electrical continuity between the electrode and the external application with which the generator is associated. This current output can be the container of the generator or a current output terminal.
The generator housing has holes receiving devices allowing the electrochemical bundle and its environment to be connected to the outside, such as current input and output terminals and a safety device in the case of internal overpressure. The generator housing can also have a hole for the introduction of a liquid electrolyte.
The terminals of an electrochemical generator have a double function: on the one hand to ensure electrical continuity between the electrodes of the electrochemical generator and the external application with which it is associated, on the other hand to contribute to the tightness of the generator's closure. The terminal passes through the wall of the container of the generator: the part situated outside the container receives the connections originating from the application, the part situated inside is connected to the electrodes. This terminal can be integral with or mounted on the container. When it is mounted on the container, a sealing and electrical insulation gasket is usually provided between the current output and the container of the generator. The so-called “glass-metal bushing” (GMB) type terminals are constituted by a central metal slug ensuring electrical continuity, surrounded by a glass gasket, tightly connected on the one hand to the central slug, and on the other hand to the wall of the container, for example the cover, into which the terminal is inserted. These GMB terminals are generally small in size, and the central slug has a diameter smaller than its length. By way of example, its diameter is comprised between 1.5 and 2 mm and its length is comprised between 5 and 8 mm, the diameter of the terminal being comprised between 10 and 17 mm.
There are several ways of electrically coupling an electrode to a current output terminal One of these ways is the use of a thin conducting strip or thin metal band, one end of which is welded to the edge of the collector of the electrode and the other end is welded to the part of the terminal situated inside the container. In practice, in order to connect an electrode to a current output, for example to a terminal which passes through a cover, the end of the thin strip is positioned, held and fixed on the internal part of the terminal. The generator is then closed using the cover.
When the electrochemical generator contains a liquid electrolyte, it is necessary to provide a filler hole, generally in the cover. In the case of generators which are small in size, this hole can be arranged on the actual inside of the current output terminal, in order to gain space on the cover. This is the case for example of the generator described by the document JP-60,023,970 which comprises a hollow GMB terminal in order to allow the introduction of the electrolyte. The filler hole is then closed by a rod inserted into the tube, then narrowing of the tube is carried out by caulking, finally the hole is sealed by laser welding. The electric coupling is carried out by a connection fixed to the lateral cylindrical surface of the internal part of the slug.
In this embodiment, the positioning of the thin strip vis-a-vis the internal part of the terminal as well as holding it before its fixing proves awkward. The closing of the cover then engenders a complex folding of the connection. During this operation, there is a risk of damaging the fixing of the thin strip to the terminal, or even the thin strip itself. The resultant risks are on the one hand the occurrence of short-circuits and on the other hand the closure of the lower part of the electrolyte filler hole.